Organ regeneration promises unlimited access to replacement tissues. The current paradigm of organ regeneration is dependent on transplantation of adult tissue-restricted stem and progenitor cells to repair the damaged organ. However, healing injured organs often leads to fibrosis with little recovery of function. This proposal challenges the prevailing viewpoint and tests an alternative complimentary approach that regeneration could also be directed by tissue-specific vascular endothelial cells (ECs) functioning as an instructive niche to promote organ regeneration and repair without provoking maladaptive fibrosis. This notion is based on our finding that blood vessels are not just the passive plumbing for delivery of oxygen and nutrients, but are active participants in organ function. Indeed, our group has pioneered the transformative concept that tissue-specific ECs produce a defined set of non- fibrotic paracrine mediators, called Angiocrine Factors to directly induce organ regeneration without fibrosis. Yet, regenerative function and the repertoire of angiocrine factors elaborated by ECs depend upon the organ from which they originate. Indeed, the molecular determinants of angiocrine heterogeneity are unknown. Thus, we hypothesize that generic, unspecified, ECs acquire tissue specific function by a process of in vivo education wherein extra-vascular cues trigger transcriptional programs. Specified ECs are credentialed to deploy tissue-specific angiocrine growth factors that drive organ repair without aberrant pro-fibrotic remodeling. Our objective here is to identify transcription factors (TFs) regulating tissue-specification of EC angiocrine function so that generic ECs can be programmed to target particular vascular beds to promote regeneration. To test this transformative hypothesis and translate these concepts for clinical use we will address the following objectives: Aim 1) Identify molecular determinants of vascular heterogeneity and organotypic regenerative function; Aim 2) Determine and validate the molecular signals and angiocrine factors elaborated by tissue-specific ECs that promote organ repair without provoking fibrosis. We have developed technologies to propagate generic ECs derived from mouse and human pluripotent stem cells and those ECs transcriptionally reprogrammed from amniotic cells. The proposed work is expected to overturn the scientific conceptualization of a monofunctional, inert, microvasculature by revealing a dynamic, tissue-specified role for ECs in organ repair. Successful completion of the proposed studies will enable therapeutic use of educated, tissue-specified ECs that home to their native injured organs and supply tissue-specific angiocrine signals to orchestrate organ regeneration. Alternatively, once known the angiocrine factors could be delivered directly. This transformative approach opens new therapeutic avenues of research to stimulate organ repair without scarring.